Loose nanofiltration membrane custom-tailored for resource recovery

Compared to the traditional nanofiltration (NF) membrane with molecular weight cut-off (MWCO) below 500 Da, an emerging loose NF (LNF) membrane with MWCO of 500 ~ 2000 Da has attracted increasing interests due to its higher selectivity and lower operating pressure, which exhibited distinct advantages in resource recovery from biomass and wastewater. This review summarizes the development of the LNF membranes, focusing on their preparations and applications. Regarding the membrane preparation, phase inversion and interfacial polymerization are the two leading and scalable fabrication methods, and other methods including dip coating, mussel-inspired deposition, self-assembly, grafting polymerization, and nanomaterials assembly/growth are also widely studied at a laboratory scale. As for the application of LNF, the fractionation of saccharides, polyphenols, and pigments for bioresource recovery as well as the separation of dyes and salts for “zero discharge” become research hotspots due to the increasing industrial demand. Besides the existing challenges faced by the applications of LNF, many opportunities to advance the field are also pointed out. This review not only provides a comprehensive overview on the development of the LNF membrane but also offers guidance to improve the membrane separation performance, especially for the resource recovery to minimize environmental pollution.